A Cretaceous Gondwana origin of the wax palm subfamily (Ceroxyloideae: Arecaceae) and its paleobiogeographic context

Abstract

Here we study a well-preserved petrified palm stem from the latest Maastrichtian (Late Cretaceous) to earliest Danian (early Paleocene) sediments (c. 66–65 Ma old) of the Deccan Intertrappean Beds of Madhya Pradesh, Central India. We infer its systematic relationships and relevance to palm evolution. The significant anatomical attributes of the fossil include the presence of fibrovascular bundles (fvbs) with reniform dorsal fibrous sclerenchyma (dcap), 2 to >4 metaxylem vessel elements in each fvb, lacunar ground parenchyma tissue, and centrifugal differentiation of the fibrous dcap parts of the fvbs. These features reveal a close resemblance to extant taxa of the wax palm subfamily Ceroxyloideae, now with a disjunct distribution in America, Australia, Madagascar and the Comoros. The Cretaceous stem is described here as Palmoxylon ceroxyloides Khan, Hazra et Bera, sp. nov. This is the oldest reliable occurrence of Ceroxyloideae in the fossil record. Present fossil evidence indicates that the sub-family was already present in India in the Late Cretaceous (Maastrichtian), about 10–15 million years before the collision of India with Eurasia. Post-collision the subfamily may have been dispersed to East Asia and then to North America via the Bering land bridge (BLB), finally reaching South America via the Isthmus of Panama link during the Miocene. However, the present-day distribution of Ceroxyloideae in Australia, Madagascar and Comoros may be explained by a historical long-distance dispersal (LDD) hypothesis.